Rotor position sensing system for permanent magnet synchronous motors and related methods

ABSTRACT

Implementations of a system for sensing rotor position of a PMSM may include: a controller which may be coupled with the PMSM. The controller may be configured to apply a plurality of voltage vectors to the PMSM to generate a plurality of sensing signals from a stator of the PMSM in response. A comparator may be coupled to the PMSM configured to receive and to compare each one of the plurality of sensing signals with a threshold voltage. A rise time measurement circuit may calculate a plurality of rise times using the plurality of sensing signals in response to receiving a signal from the comparator. The rotor-angle estimation circuit may be configured to identify from the plurality of rise times a shortest rise time and a voltage vector corresponding with the shortest rise time and thereby identify the position of the rotor of the PMSM.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of the earlier U.S.Utility patent application to Masanori Okubayashi entitled “RotorPosition Sensing System for Permanent Magnet Synchronous Motors andRelated Methods,” application Ser. No. 15/382,160, filed Dec. 16, 2016,now pending, the disclosure of which is hereby incorporated entirelyherein by reference.

BACKGROUND

1. Technical Field

Aspects of this document relate generally to permanent magnetsynchronous motors. More specific implementations involve rotor positiondetection of permanent magnet synchronous motors.

2. Background

Torque in a permanent magnet synchronous motor is created by applyingout of phase currents to the stator or field windings of the motor. Theout of phase currents create a magnetic flux in the motor which resultsin the rotation of a magnetic rotor. The amount of torque is controlledby the out of phase currents applied and the position of the magneticrotor. Various conventional position sensing systems for permanentmagnet synchronous motors are disclosed in U.S. Patent ApplicationPublication No. 2010/0181952 to Kuang-Yao Cheng, entitled “Initial rotorposition detection for permanent magnet synchronous motors,” publishedJul. 22, 2010 and in U.S. Pat. No. 5,028,852 to John C. Dunfieldentitled “Position detection for a brushless DC motor without halleffect devices using a time differential method,” issued Jul. 2, 1991,the disclosures of each of which are hereby incorporated entirely hereinby reference.

SUMMARY

Implementations of a system for sensing rotor position of a permanentmagnet synchronous motor (PMSM) may include: a controller which may becoupled with the PMSM. The controller may be configured to apply aplurality of voltage vectors to the PMSM to generate a plurality ofsensing current signals from a stator of the PMSM in response. Aresistor may be coupled to the stator of the PMSM. The resistor may beconfigured to receive the plurality of sensing current signals andgenerate a corresponding plurality of sensing voltage signals. Anamplifier may be coupled to the resister. The amplifier may beconfigured to receive and to amplify the plurality of the sensingvoltage signals. A comparator may be coupled to the amplifier and to athreshold voltage generator. The comparator may be configured to receiveand to compare each one of the plurality of amplified sensing voltagesignals with a threshold voltage generated by the threshold voltagegenerator. A rise time measurement circuit may be coupled to thecomparator. The rise time measurement circuit may be configured tocalculate a plurality of rise times using the plurality of amplifiedsensing voltage signals in response to receiving a signal from thecomparator. A memory may be coupled with the rise time measurementcircuit, which may be configured to store the plurality of rise times. Arotor-angle estimation circuit may be coupled with the memory. Therotor-angle estimation circuit may be configured to identify from theplurality of rise times a shortest rise time and a voltage vectorcorresponding with the shortest rise time. The rotor-angle estimationcircuit may identify at least two adjacent voltage vectors to thevoltage vector with the shortest rise time. The rotor-angle estimationcircuit may average, sum or weighted sum the rise times of the voltagevector corresponding with the shortest rise time and its at least twoadjacent voltage vectors to form an average first rise time value, asummed first rise time value, or a weighted summed first rise timevalue, respectively. The rotor-angle estimation circuit may identify thevoltage vector that is 180 degrees out of phase with the voltage vectorcorresponding to the shortest rise time. The rotor-angle estimationcircuit may identify at least two adjacent voltage vectors to thevoltage vector that is 180 degrees out of phase. The rotor-angleestimation circuit may average, sum, or weighted sum the rise times ofthe voltage vector that is 180 degrees out of phase and its at least twoadjacent voltage vectors to form a second average rise time value, asummed second rise time value, or a weighed summed second rise timevalue, respectively. The rotor-angle estimation circuit may calculate arotor position relative to the stator of the PMSM through identifying alowest average rise time, a lowest summed rise time, or a lowestweighted summed rise time using the corresponding pair of the firstaverage rise time value, the second average rise time value, the summedfirst rise time value, the summed second rise time value, the weightedsummed first rise time value, or the weighted summed second rise timevalue, respectively.

Implementations of a system for sensing rotor position of a PMSM mayinclude one, all, or any of the following:

The threshold voltage generator may be coupled to the controller and maybe configured to generate the threshold voltage in response to a commandfrom the controller. The threshold voltage may be one of a firstthreshold voltage and a second threshold voltage.

The first threshold voltage and the second threshold voltage may becalculated using a first threshold voltage equation or a secondthreshold voltage equation. The first threshold voltage equation may beV_(th1)=(G)(R_(sh))(I_(th1))+V_(off). The second threshold voltageequation may be V_(th2)=(G)(R_(sh))(I_(th2))+V_(off) where V_(th1) isthe first threshold voltage, V_(th2) is the second threshold voltage, Gis a gain of the amplifier, R_(sh) is a resistance from the resistor,I_(th1) is a first threshold current, I_(th2) is a second thresholdcurrent, and V_(off) is the amplifier's offset voltage.

The first threshold current and the second threshold current may berelated by the equation

$I_{{th}\; 1} = {\frac{4}{3}{I_{{th}\; 2}.}}$

The plurality of voltage vectors may be one of 12 and 24.

Implementations of a system for sensing rotor position of a permanentmagnet synchronous motor (PMSM) may include: a controller which may becoupled with the PMSM. The controller may be configured to apply aplurality of voltage vectors to the PMSM to generate a plurality ofsensing current signals from a stator of the PMSM in response. Anamplifier may be coupled to the PMSM. The amplifier may be configured toreceive and to amplify the plurality of the sensing current signals. Ananalog-to-digital (A/D) converter may be coupled to the amplifier. TheA/D converter may be configured to convert the plurality of the sensingcurrent signals into a plurality of digital current signals. The risetime measurement circuit may be coupled to the A/D converter and to acontroller. The rise time measurement circuit may be configured tocalculate a plurality of rise times in response to receiving a pluralityof digital current signals from the A/D converter and a threshold A/Dvalue from the controller. A memory may be coupled with the rise timemeasurement circuit. The memory may be configured to store the pluralityof rise times. A rotor-angle estimation circuit may be coupled with thememory. The rotor-angle estimation circuit may be configured to identifyfrom the plurality of rise times a shortest rise time and a voltagevector corresponding with the shortest rise time. The rotor-angleestimation circuit may identify at least two adjacent voltage vectors tothe voltage vector with the shortest rise time. The rotor-angleestimation circuit may average, sum or weighted sum the rise times ofthe voltage vector corresponding with the shortest rise time and its atleast two adjacent voltage vectors to form an average first rise timevalue, a summed first rise time value, or a weighted summed first risetime value, respectively. The rotor-angle estimation circuit mayidentify the voltage vector that is 180 degrees out of phase with thevoltage vector corresponding to the shortest rise time. The rotor-angleestimation circuit may identify at least two adjacent voltage vectors tothe voltage vector that is 180 degrees out of phase. The rotor-angleestimation circuit may average, sum, or weighted sum the rise times ofthe voltage vector that is 180 degrees out of phase and its at least twoadjacent voltage vectors to form a second average rise time value, asummed second rise time value, or a weighted summed second rise timevalue, respectively. The rotor-angle estimation circuit may calculate arotor position relative to the stator of the PMSM by determining alowest average rise time, a lowest summed rise time, or a lowest weighedsummed rise time using the corresponding pair of the first average risetime value, the second average rise time value, the summed rise timevalue, the summed second rise time value, the weighted summed first risetime value, or the weighted summed rise time value, respectively.

Implementations of a system for sensing rotor position of a PMSM mayinclude one, all, or any of the following:

The controller may be configured to generate a first threshold currentand a second threshold current. The first threshold current and thesecond threshold current may be related by the equation

${I_{{th}\; 1} = {\frac{4}{3}I_{{th}\; 2}}},$where I_(th1) is the first threshold current and I_(th2) is the secondthreshold current.

The controller may be configured to generate a first A/D threshold valueand a second A/D threshold value using a first A/D threshold valueequation or a second A/D threshold value equation. The first A/Dthreshold value equation may be

${AD}_{{th}\; 1} = {V_{{th}\; 1}\left( \frac{2^{n}}{{Vref}_{AD}} \right)}$and the second A/D threshold value equation may be

${AD}_{{th}\; 2} = {V_{{th}\; 2}\left( \frac{2^{n}}{{Vref}_{AD}} \right)}$where AD_(th1) is the first A/D threshold value, AD_(th2) is the secondA/D threshold value, V_(th1) is a first threshold voltage, V_(th2) is asecond threshold voltage, n is the A/D resolution, and Vref_(AD) is afull scale voltage value.

The rise time measurement circuit may measure each rise time using arise time measurement equation. The rise time measurement equation maybe

$T_{r} = {{\left( \frac{{AD}_{th} - {AD}_{1}}{{AD}_{2} - {AD}_{1}} \right)\left( {t_{2} - t_{1}} \right)} + t_{1}}$where T_(r) is the rise time, AD_(th) is one of the first A/D valuethreshold and the second A/D value threshold, AD₂ is a first value fromthe A/D converter formed when AD₂ exceeds AD_(th), AD₁ is a second valuefrom the A/D converter formed prior to AD₁ exceeding AD_(th), t₂ is atime corresponding with AD₂, and t₁ is a time corresponding with AD₁.

The plurality of voltage vectors may be one of 12 and 24.

Implementations of a method for sensing rotor position of a permanentmagnet synchronous motor (PMSM) may include applying a plurality ofvoltage vectors to a stator of a PMSM. The method may include generatinga plurality of sensing current signals from the stator in response tothe plurality of voltage vectors applied to the PMSM. The plurality ofsensing current signals may be converted into a plurality of sensingvoltage signals using a resistor coupled to the stator. The method mayinclude amplifying the plurality of sensing voltage signals using anamplifier coupled to the resistor. Each of the amplified plurality ofsensing voltage signals may be compared with a threshold voltagegenerated by a threshold voltage generator using a comparator coupled tothe amplifier. The method may include calculating a plurality of risetimes using the amplified plurality of sensing voltage signals and asignal from the comparator using a rise time measurement circuit coupledto the comparator. The method may include storing the plurality of risetimes in a memory coupled with the rise-time measurement circuit. Themethod of determining a rotor position relative to the stator of thePMSM may include using a rotor-angle estimation circuit by identifyingfrom the plurality of rise times a shortest rise time and a voltagevector corresponding with the shortest rise time, identifying at leasttwo adjacent voltage vectors to the voltage vector with the shortestrise time, and averaging, summing, or weighted summing the rise times ofthe voltage vector corresponding with the shortest rise time and its atleast two adjacent voltage vectors to form an average first rise timevalue, a summed first rise time value, or a weighted summed first risetime value, respectively. The method may include using the rotor angleestimation circuit to determine the rotor position by identifying thevoltage vector that is 180 degrees out of phase with the voltage vectorcorresponding to the shortest rise time, identifying at least twoadjacent voltage vectors to the voltage vector that is 180 degrees outof phase, and averaging, summing, or weighted summing the rise times ofthe voltage vector corresponding with the voltage vector that is 180degrees out of phase and its at least two adjacent voltage vectors toform a second average rise time value, a summed second rise time value,or a weighted summed second rise time value, respectively. The methodmay include calculating the rotor position relative to the stator bydetermining a lowest average rise time, a lowest summed rise time, or alowest weighted summed rise time using the corresponding pair of thefirst average rise time value, the second average rise time value, thesummed first rise time value, the summed second rise time value, theweighted summed first rise time value, or the weighted summed secondrise time value, respectively.

Implementations of a method for sensing rotor position of a PMSM mayinclude one, all, or any of the following:

Generating a threshold voltage may include using the threshold voltagegenerator in response to a command from the controller coupled with thethreshold voltage generator. The threshold voltage may be generated asone of a first threshold voltage and a second threshold voltage.

Calculating the first threshold voltage and the second threshold voltagemay include using a first threshold voltage equation or a secondthreshold voltage equation. The first threshold voltage equation may beV_(th1)=(G)(R_(sh))(I_(th1))+V_(off). The second threshold voltageequation may be V_(th2)=(G)(R_(sh))(I_(th2))+V_(off) where V_(th1) isthe first threshold voltage, V_(th2) is the second threshold voltage, Gis a gain of the amplifier, R_(sh) is a resistance from the resistor,I_(th1) is a first threshold current, I_(th2) is a second thresholdcurrent, and V_(off) is the amplifier's offset voltage.

Calculating the first threshold voltage and the second threshold voltageusing a first threshold current and a second threshold current mayinclude using a first threshold current and a second threshold currentrelated by the equation

$I_{{th}\; 1} = {\frac{4}{3}{I_{{th}\; 2}.}}$

Applying a plurality of voltage vectors may include applying one of 12and 24 voltage vectors.

Implementations of a method for sensing rotor position of a permanentmagnet synchronous motor (PMSM) may include applying a plurality ofvoltage vectors to a stator of a PMSM. The method may include generatinga plurality of sensing current signals from the stator in response tothe plurality of voltage vectors applied to the PMSM. The method mayinclude amplifying the plurality of sensing current signals using anamplifier coupled to the PMSM. The amplified plurality of sensingcurrent signals may be converted into a plurality of digital currentsignals using an analog to digital (A/D) converter coupled with theamplifier. The method may include calculating a plurality of rise timesusing a rise-time measurement circuit coupled to the A/D converter andto a controller, based upon the plurality of digital current signalsreceived from the A/D converter and an A/D threshold value from thecontroller. The method may include storing the plurality of rise timesin a memory coupled with the rise-time measurement circuit. The methodmay include determining a rotor position relative to the stator of thePMSM using a rotor-angle estimation circuit by identifying from theplurality of rise times a shortest rise time and a voltage vectorcorresponding with the shortest rise time, identifying at least twoadjacent voltage vectors to the voltage vector with the shortest risetime, and averaging, summing, or weighted summing the rise times of thevoltage vector corresponding with the shortest rise time and its atleast two adjacent voltage vectors to form an average first rise timevalue, a summed first rise time value, or a weighted summed first risetime value, respectively. The method of determining the rotor positionmay include identifying the voltage vector that is 180 degrees out ofphase with the voltage vector corresponding to the shortest rise time,identifying at least two adjacent voltage vectors to the voltage vectorthat is 180 degrees out of phase, and averaging, summing, or weightedsumming the rise times of the voltage vector corresponding with thevoltage vector that is 180 degrees out of phase and its at least twoadjacent voltage vectors to form a second average rise time value, asummed second rise time value, or a weighted summed second rise timevalue. The method may include calculating the rotor position relative tothe stator by determining a lowest average rise time, a lowest summedrise time, or a lowest weighted summed rise time using the correspondingpair of the first average rise time value, the second average rise timevalue, the summed first rise time value, the summed second rise timevalue, the weighted summed first rise time value, or the weighted summedsecond rise time value, respectively.

Implementations of a method for sensing rotor position of a PMSM mayinclude one, all, or any of the following:

Generating a first threshold current and a second threshold current mayinclude using the controller. The first threshold current and the secondthreshold current may be related by the equation

$I_{{th}\; 1} = {\frac{4}{3}I_{{th}\; 2}}$where I_(th1) is me first threshold current and I_(th2) is the secondthreshold current.

Measuring each rise time with the rise time measurement circuit mayinclude using a rise time measurement equation. The rise timemeasurement equation may be

$T_{r} = {{\left( \frac{{AD}_{th} - {AD}_{1}}{{AD}_{2} - {AD}_{1}} \right)\left( {t_{2} - t_{1}} \right)} + t_{1}}$where T_(r) is the rise time, AD_(th) is one of the first A/D valuethreshold and the second A/D value threshold, AD₂ is a first value fromthe A/D converter formed when AD₂ exceeds AD_(th), AD₁ is a second valuefrom the A/D converter formed prior to AD₁ exceeding AD_(th), t₂ is atime corresponding with AD₂, and t₁ is a time corresponding with AD₁.

Applying a plurality of voltage vectors may include applying one of 12and 24 voltage vectors.

The foregoing and other aspects, features, and advantages will beapparent to those artisans of ordinary skill in the art from theDESCRIPTION and DRAWINGS, and from the CLAIMS.

BRIEF DESCRIPTION OF THE DRAWINGS

Implementations will hereinafter be described in conjunction with theappended drawings, where like designations denote like elements, and:

FIG. 1 is an illustration of two sets of voltage vectors;

FIG. 2 is a graph illustrating the relation between the electricalangles of voltage vectors and resulting inductance;

FIG. 3 is an illustration of a three phase PMSM;

FIGS. 4A-4D are graphs of FIG. 2 with voltage vectors plotted thereon;

FIG. 5 is an illustration of an equivalent circuit of a three phasemotor;

FIG. 6 is an illustration of the impulse response of an RL seriescircuit;

FIGS. 7-8 are simplified equivalent inductance and impedance circuits ofFIG. 5;

FIG. 9 is a graph with 12 voltage vectors plotted thereon;

FIG. 10 is a representation of the relation of the plotted voltagevectors of FIG. 9 with the rotor position of a PMSM;

FIG. 11 is a graph of the plotted voltage vectors of FIG. 9 withshort-rise-time voltage vectors grouped together;

FIG. 12 is a flow chart showing the use of summed data to calculaterotor position.

FIG. 13 is a flow chart showing the use of summed data using weightedcoefficients to calculate rotor position.

FIG. 14 is a block diagram of a first implementation of a system forsensing the rotor position of a PMSM;

FIG. 15 is a waveform diagram of the circuit represented in FIG. 14.

FIG. 16 is a block diagram of an implementation of a system for sensingthe rotor position of a PMSM; and

FIG. 17 is a waveform diagram of the circuit represented in FIG. 16.

DESCRIPTION

This disclosure, its aspects and implementations, are not limited to thespecific components, assembly procedures or method elements disclosedherein. Many additional components, assembly procedures and/or methodelements known in the art consistent with the intended rotor positionsensing system will become apparent for use with particularimplementations from this disclosure. Accordingly, for example, althoughparticular implementations are disclosed, such implementations andimplementing components may comprise any shape, size, style, type,model, version, measurement, concentration, material, quantity, methodelement, step, and/or the like as is known in the art for such rotorposition sensing systems, and implementing components and methods,consistent with the intended operation and methods.

Referring now to FIG. 1, two sets of voltage vectors are shown. In thisimplementation, the total twelve voltage vectors used in various systemimplementations disclosed herein are divided into two groups, 2, 4. Eachvoltage vector is labeled using a voltage vector reference labeledbetween (1) and (12). The twelve voltage vectors are applied to apermanent magnet synchronous motor (PMSM) during operation, and whenthey are applied, each voltage vector induces currents in the statorwindings of the PMSM.

FIG. 2 is a graph illustrating the relationship between the twelvevoltage vectors' varying electrical angles and the inductance of theresulting induced current caused by each vector. FIG. 3 is a diagram ofthe stator windings represented by inductors for a three-phase PMSM. Avoltage vector that is aligned with the north pole (a) of the magneticrotor 6 corresponds with the value of the lowest inductance shown bypoint (a) in FIG. 2. A voltage vector aligned with the south pole (b) ofthe magnetic rotor 6 in FIG. 3 corresponds with the point (b) in FIG. 2.While voltage vectors that align with the north and south poles of themagnetic rotor 6 both result in low inductances, the lowest inductancevalue observed corresponds to the voltage vector most closely alignedwith the north pole.

Referring to FIGS. 4A and 4C, the inductance induced after applying sixvoltage vectors to the stator windings of a PMSM in a worst case (FIG.4A) and in a best case (FIG. 4C) situation is illustrated. As can beseen, in the worst case situation in FIG. 4A, the ability of the systemto be able to find/estimate the electrical angle in degrees of thelowest inductance point is poor, as the data values corresponding withthe vectors applied on the side of the curve around 60 degrees are onlyslightly higher in inductance than the data values corresponding withthe vectors applied on the side of the curve around 240 degrees. Becauseof this, the noise margin, or the range of inductance values in whichthe system can detect the correct lowest possible inductance value inthe midst of normal measurement noise, is narrow. Where measurementnoise causes the data values around 60 degrees to have basically thesame inductance values as those around 240 degrees, the system wouldhave no way of accurately calculating the lowest inductance value.Because of this, it is evident that merely using 6 voltage vector drivendata points to try to identify the lowest inductance value can beproblematic. Referring to FIGS. 4B and 4D, graphs of induced inductancevalues using twelve voltage vectors that correspond with the graphs inFIGS. 4A and 4C are illustrated. As before, FIG. 4B illustrates theworst case and FIG. 4D illustrates the best case. In the worst case,because of the increase in data points the noise margin can be observedto be larger, meaning that with 12 vectors, the increase in data givesthe system a better chance of detecting/estimating the lowest inductancevalue. This is true even in the best case scenarios, where the systemhas actually identified the two absolute lowest inductance values using6 vectors and using 12 vectors. This is because the additional datapermits the system to more accurately know that the system has indeedfound the lowest inductance point.

The importance of being able to find the lowest inductance point isimportant, because that lowest inductance point corresponds with anelectrical angle value which corresponds with the physical position ofthe rotor of the PMSM. Knowing as accurately as possible the electricalangle value, then, permits the system to know as accurately as possiblethe physical position of the rotor at any given time.

FIG. 5 is an illustration of a model of a circuit for a three phasemotor. A PMSM can be modeled as a three-phase RL series circuit. FIG. 6illustrates the equivalent circuit on the left and then graphs of thevoltage (center) and current (right side) impulse response of the RLseries circuit. Based on the equivalent circuit, the current asillustrated in FIG. 6 can be expressed as

$\begin{matrix}{I = {\frac{V_{DC}}{R}\left( {1 - e^{{- \frac{R}{L}}t}} \right)}} & {{Eq}.\mspace{14mu} 1}\end{matrix}$where I represents the current, V_(DC) represents the DC link voltage, Rrepresents equivalent resistance corresponding to the applied voltagevectors, L represents the inductance, and t represents the time.

In graph 16 of FIG. 6, T_(r) is the rise time, or the time until thecurrent reaches a threshold value I_(th). Thus, equation 1 can berearranged and T_(r) can be expressed as

$\begin{matrix}{T_{r} = {{- \frac{L}{R}}{\ln\left( {1 - \frac{{RI}_{th}}{V_{DC}}} \right)}}} & {{Eq}.\mspace{14mu} 2}\end{matrix}$Equation 2 shows that Tr is proportional to L when R, V, and I_(th) areconstant. Therefore, if the lowest inductance can be detected from thecurrent sensing signal, the lowest rise time can also be detected.

The equivalent circuit illustrated in FIG. 6 can be simplified to theequivalent inductance and impedance circuits illustrated in FIG. 7 andFIG. 8. FIG. 7 is an equivalent inductance and impedance circuitcorresponding to the circuit encountered by voltage vectors of group 2of FIG. 1 applied to a PMSM, expressed as equation 3, where L_(eq1) is afirst equivalent inductance, L₁ is a first inductance, R_(eq1) is afirst equivalent impedance, and R is an impedance.

$\begin{matrix}{{L_{{eq}\; 1} = {\frac{3}{2}L_{1}}},{R_{{eq}\; 1} = {\frac{3}{2}R}}} & {{Eq}.\mspace{14mu} 3}\end{matrix}$

FIG. 8 is the equivalent inductance and impedance circuit correspondingto the circuit encountered by voltage vectors of group 4 of FIG. 1applied to a PMSM, expressed as equation 4, where L_(eq2) is a secondequivalent inductance, L₂ is a second inductance, R_(eq2) is a secondequivalent impedance, and R is an impedance.L_(eq2)=2L₂,R_(eq2)=2R  Eq. 4

When the rotor flux is ignored and L₁ equals L₂, the relationshipbetween L_(eq1) and L_(eq2) is shown by equation 5.

$\begin{matrix}{{L_{{eq}\; 1} = {\frac{3}{4}L_{{eq}\; 2}}},\;{R_{{eq}\; 1} = {\frac{3}{4}R_{{eq}\; 2}}}} & {{Eq}.\mspace{14mu} 5}\end{matrix}$

If the rise time can be calculated by inserting the equivalentinductance and equivalent impedance values from equation 3 and 4 intoequation 2, equations 6 and 7 result.

$\begin{matrix}{T_{r\; 1} = {{- \frac{L_{1}}{R}}{\ln\left( {1 - \frac{3\text{/}2{RI}_{th}}{V_{DC}}} \right)}}} & {{Eq}.\mspace{14mu} 6} \\{T_{r\; 2} = {{- \frac{L_{2}}{R}}{\ln\left( {1 - \frac{2{RI}_{th}}{V_{DC}}} \right)}}} & {{Eq}.\mspace{14mu} 7}\end{matrix}$

As can be seen by equations 6 and 7, the first rise time T_(r1) and thesecond rise time T_(r2) are not equal even when L₁ equals L₂. Therefore,a simple comparison of the value of T_(r1) and T_(r2) does not lead to aproper comparison of the value of L₁ and L₂, and in turn, does notindicate the rotor position of the PMSM. By using different currentthreshold values, however, this issue can be resolved.

If I_(th1) is the current threshold used in association with the voltagevectors of group 2 from FIG. 1, and I_(th2) is the current thresholdused in association with the voltage vectors of group 4 from FIG. 1, amathematical relationship between a first and second current thresholdcan be rewritten as equation 8.

$\begin{matrix}{I_{{th}\; 1} = {\frac{4}{3}I_{{th}\; 2}}} & {{Eq}.\mspace{14mu} 8}\end{matrix}$

Substituting the relationship in equation 8, equations 6 and 7 can berewritten as equations 9 and 10.

$\begin{matrix}{T_{r\; 1} = {{{- \frac{L_{1}}{R}}{\ln\left( {1 - \frac{3\text{/}2{RI}_{th}}{V_{DC}}} \right)}} = {{{- \frac{L_{1}}{R}}{\ln\left( {1 - \frac{3\text{/}2{R4}\text{/}3I_{{th}\; 2}}{V_{DC}}} \right)}} = {{- \frac{L_{1}}{R}}{\ln\left( {1 - \frac{2{RI}_{{th}\; 2}}{V_{DC}}} \right)}}}}} & {{Eq}.\mspace{14mu} 9} \\{\mspace{79mu}{T_{r\; 2} = {{- \frac{L_{2}}{R}}{\ln\left( {1 - \frac{2{RI}_{{th}\; 2}}{V_{DC}}} \right)}}}} & {{Eq}.\mspace{14mu} 10}\end{matrix}$By varying the threshold currents, the rise times corresponding to allvoltage vectors in both groups can now be compared on a same basis,permitting detection of the lowest inductance value through using therise times of each voltage vector. Equations 9 and 10 may be used toconfirm that the rise times are proportional to the coil inductances ofeach voltage vector by ensuring that the proper current threshold isselected.

FIG. 9 represents a graph of the relationship between the rise times andthe corresponding electrical angles of twelve voltage vectors for aparticular implementation of a PMSM. FIG. 10 is a representation of howthe plotted voltage vectors of FIG. 9 would relate to rotor position ofa PMSM. The voltage vector (10) with the lowest rise time in FIG. 9corresponds to the position of the north pole of the PMSM within about30 degrees as illustrated by the vector diagram of FIG. 10.

To gain more noise immunity when using the vector data to find thelowest rise time, it is effective to use averaged data or summed datawhen determining the rotor position of a PMSM. FIG. 11 is a graph of theplotted voltage vectors of FIG. 9 with voltage vectors combined togetherto form groups 22 and 24. FIG. 12 is a flow chart of an implementationof determining the rotor position using summed data. As indicated byblock 82 in FIG. 12, the shortest measured rise time, A2 correspondingwith voltage vector (10) of FIG. 11 in this implementation, is summedwith adjacent rise time values A1 and A3, corresponding with voltagevectors (9) and (11) of FIG. 11, as indicated by block 86 of FIG. 12. Asindicated by block 84 of FIG. 12, B2 is the rise time of the voltagevector 180 degrees out of phase from the voltage vector with theshortest measured rise time. In the implementation illustrated by FIG.11, voltage vector (4) is the voltage vector 180 degrees out of phasefrom the voltage vector with the shortest measured rise time (10). Inthis implementation B2 is summed with rise times B1 and B3 correspondingwith voltage vectors (3) and (5) of FIG. 11, as indicated by block 88 ofFIG. 12. By comparing the sum of the rise time values of group 22 withthe sum of the rise time values of group 24 as indicated by block 90,the true lowest rise time may be determined. If the sum of group 22,Asum, is less than the sum of group 24, Bsum, then the voltage vectorwith the shortest measured rise time is the vector correlating with thenorth pole of the rotor as indicated by block 92 of FIG. 12. If on theother hand the sum of group 24, Bsum, is less than the sum of group 22,Asum, then the voltage vector that is 180 degrees out of phase from thevoltage vector with the shortest measured rise time represents the northpole of the rotor as indicated by block 94.

FIG. 13 is a flowchart of another implementation similar to theimplementation illustrated in FIG. 12, however, weighted coefficients,as indicated by blocks 100 and 102 of FIG. 13, are used to determine thetrue shortest rise time of the voltage vectors.

In still other implementations, averaged data may be used to calculatethe shortest rise time. The average data to be compared can be expressedas equation 11, where A_(ave) is the average first rise time value,A₁-A₃ are the rise times of the voltage vector with the shortest risetime and its two adjacent voltage vectors, and B_(ave) is the averagesecond rise time value and B₁-B₃ are the rise times of the voltagevectors 180 degrees out of phase from the voltage vector with theshortest rise time and its two adjacent voltage vectors.

$\begin{matrix}{{A_{ave} = \frac{\left( {A_{1} + A_{2} + A_{3}} \right)}{3}},{B_{ave} = \frac{\left( {B_{1} + B_{2} + B_{3}} \right)}{3}}} & {{Eq}.\mspace{14mu} 11}\end{matrix}$By comparing A_(ave) with B_(ave) in a similar manner as the summed datawas compared in FIGS. 12 and 13, the rotor position may be determined.If A_(ave) is less than B_(ave), then the shortest measured rise timeout of A₁-A₃ represents the north pole of the rotor. If B_(ave) is lessthan A_(ave), then the rise time 180 degrees out of phase from theshortest measured rise time represents the north pole of the rotor.

In alternative implementations, averaged data may be used by comparingthe average of the rise time values of group 22 with the average of therise time value corresponding with voltage vector (10) and with adjacentrise time values corresponding with voltage vectors (9) and (11), thefact that the rise time value corresponding with voltage vector (10) isthe lowest rise time value can be confirmed. In various implementations,the rise time value corresponding with voltage vector (10) is thencompared with the value of the rise time corresponding with a voltagevector in group 24 that is 180 degrees out of phase from the rise timevalue corresponding to voltage vector (10). Similarly, the lowest risetime value in group 24 is determined by comparing the average of theshortest rise time value of group 24 with the rise time value 180degrees out of phase (rise time value corresponding with voltage vector(4)) and with the two adjacent rise time values corresponding withvoltage vectors (3) and (5). If using the averaging process and thesubsequent 180-degree comparison process, the rise time valuecorresponding to voltage vector (10) indeed represents the lowest risetime value, the position of the north pole of the magnet of the rotorhas been identified.

In various implementations, more than two adjacent voltage vectors maybe included in the analysis in each group. In such implementations, theadjacent voltage vectors would include those close to and not just nextto the point of interest.

Referring now to FIG. 14, a block diagram of a first implementation of asystem for sensing a rotor position of a PMSM is illustrated. In thisimplementation, a controller 38 may include a state control circuit 40and a voltage vector generator 42 operatively coupled together. Thecontroller 38 is coupled with a PMSM 44.

The controller 38 is designed to generate a plurality of voltage vectorswhich may be applied to the PMSM 44, including the twelve voltagevectors used for position sensing. In a particular implementation,twelve out-of-phase voltage vectors are generated, however, in variousimplementations twenty-four or additional numbers of voltage vectors maybe applied to the PMSM 44. In response to the voltage vectors applied tothe stator windings of the PMSM 44, a plurality of current sensingsignals is generated.

A resistor 46 may be coupled with the stator windings PMSM 44, which maybe a shunt resistor in various implementations. The resistor 46 may beconfigured to receive a plurality of current sensing signals and thengenerate a corresponding plurality of sensing voltage signals. Asillustrated, an amplifier 48 is coupled with the resistor 46 which isdesigned to receive and to amplify the plurality of sensing voltagesignals for subsequent analog processing

The signals from the amplifier 48 are then received by a comparator 50coupled to the amplifier 48 and to a threshold voltage generator, 52.The comparator 50 receives and compares each sensing voltage signal fromthe amplifier 48 with a threshold voltage value from the thresholdvoltage generator 52.

The threshold voltage generator 52 is coupled with the controller 38and/or with the state control circuit 40 within the controller, and thecontroller and/or state control circuit 40 determines when and whatthreshold voltage is generated by the threshold voltage generator 42.The threshold voltage generator 42 may generate a single or multiplethreshold voltage values, including 1, 2, 6, 12, or 24 threshold voltagevalues, depending on the specific implementation and logic circuitryused in the comparator 50 itself. Because different voltage vectorsapplied to the PMSM 44 may result in different equivalent inductances,and because different equivalent inductances affect the rise time asshown in equations 1 and 2, the controller may adjust the thresholdvoltage to be produced based upon the particular voltage vector justapplied to the PMSM 44. This allows the magnitudes of the rise timescorresponding to all the voltage vectors to then be compared on anequivalent basis. In this specific implementation, one of two thresholdvoltages are produced and can be calculated using equation 12 orequation 13V _(th1)=(G)(R _(sh))(I _(th1))+V _(off)  Eq. 12V _(th2)=(G)(R _(sh))(I _(th2))+V _(off)  Eq. 13where V_(th1) is the first threshold voltage, V_(th2) is the secondthreshold voltage, G is a gain of the amplifier, R_(sh) is a resistancefrom the resistor, I_(th1) is a first threshold current, I_(th2) is asecond threshold current, and V_(off) is the amplifier's offset voltage.The first threshold current and the second threshold current are relatedby equation 8.

A rise time measurement circuit 54 is coupled with the comparator 50.The rise time measurement circuit 54 calculates a plurality of risetimes using the plurality of amplified sensing voltage signals and acounter. FIG. 15 is a waveform diagram of the circuit shown in FIG. 14.A voltage vector is applied by the controller at time t_(a). At t_(a),the counter value drops to zero and begins to rise as does the shuntcurrent and the amplifier output. The comparator compares the amplifieroutput to the threshold voltage V_(th). At time t_(b) the amplifieroutput is the same as the voltage of V_(th) and the comparator triggersthe end of applying the voltage vector and the counter is stopped, asindicated by 110 in FIG. 15. The counter value at 110 is the rise timeof the voltage vector applied. The counter is then reset to measure thenext voltage vector applied by the controller 38.

A memory 56 is coupled to the rise time measurement circuit 54 in orderto store the plurality of rise times calculated by the rise timemeasurement circuit 54. The memory may be any device or circuit for datastorage.

A rotor-angle estimation circuit 58 is coupled with the memory 56. Therotor-angle estimation circuit 58 determines the rotor position of thePMSM 44 by identifying from the plurality of rise times in the memory 56the voltage vector with the shortest rise time among the plurality ofrise time values stored in the memory 56. In other implementations, therotor-angle estimation circuit 58 may determine the rotor position ofthe PMSM 44 by using averaged data, summed data, or summed data usingweighted coefficients as previously disclosed in this document. Therotor-angle estimation circuit 58 is coupled with a controller 38 andcommunicates the rotor position of the PMSM 44 to the controller 38.

In various implementations, a microprocessor may be included in thesystem which may include the rotor-angle estimation circuit 58. Inparticular implementations, the microprocessor may also include thecontroller 38. In these implementations, much of the functions of thevarious components of the system may be implemented using themicroprocessor and/or as part of the microprocessor. In other variousimplementations, the rotor-angle estimation circuit 58 may include aplurality of logic circuits which act to carry out all of the functionsof the various components of the system without including amicroprocessor.

Referring now to FIG. 16, a block diagram of another implementation of asystem for sensing a rotor position of a PMSM is illustrated. In thisimplementation, a controller 60 includes a state control circuit 62 anda voltage vector generator 64. The controller 60 is coupled with a PMSM66 and is configured to generate a plurality of voltage vectors whichare applied to the PMSM 66. In a particular implementation, twelveout-of-phase voltage vectors are generated, however, in variousimplementations, twenty-four or more voltage vectors may be applied tothe PMSM 66. In response to the voltage vectors applied to the statorwindings of the PMSM 66, a plurality of current sensing signals isproduced similarly to the implementation illustrated in FIG. 14

An amplifier 68 is coupled with the resistor that generates the currentsensing signals from the stator coils of the PMSM 66. The amplifier 68receives and amplifies the plurality of sensing current signals androutes the plurality of amplified sensing current signals to ananalog-to-digital (A/D) converter 70. The A/D converter 70 then convertsthe plurality of sensing current signals into a plurality of digitalcurrent signals.

A rise-time measurement circuit 72 is coupled with the A/D converter 70,to a controller 60, and/or to a state control circuit 62 within thecontroller 60. The rise-time measurement circuit 72 calculates aplurality of rise times in response to receiving the plurality ofdigital current signals from the A/D converter 70 using an A/D thresholdvalue. In this implementation, there are two A/D threshold values thatmay be used as calculated by equations 14 and 15

$\begin{matrix}{{AD}_{{th}\; 1} = {V_{{th}\; 1}\left( \frac{2^{n}}{{Vref}_{AD}} \right)}} & {{Eq}.\mspace{14mu} 14} \\{{AD}_{{th}\; 2} = {V_{{th}\; 2}\left( \frac{2^{n}}{{Vref}_{AD}} \right)}} & {{Eq}.\mspace{14mu} 15}\end{matrix}$where AD_(th1) is the first A/D threshold value, AD_(th2) is the secondA/D threshold value, V_(th1) is a first threshold voltage, V_(th2) is asecond threshold voltage, n is the A/D resolution, and Vref_(AD) is afull scale voltage value. The calculation of the first and secondthreshold voltages are shown in equations 12 and 13. The values of thethreshold voltages are determined by the values of the thresholdcurrents. The relationship between the first and second thresholdcurrents is shown in equation 8.

FIG. 17 is a waveform diagram of the circuit of FIG. 16. FIG. 17illustrates how the rise times are measured in one implementation. Avoltage vector is applied by the controller at time t₀. Once the voltagevector is applied, the rise-time measurement circuit signals to startthe A/D converter (70). The A/D converter begins to generate sensingcurrent signals 112. When a sensing current signal exceeds the value ofthe A/D threshold value (AD_(th)), as indicated by digital currentsignal AD₂, the voltage vector is no longer applied. This occurs at timet₂. The rise time measurement section then uses four data to calculatethe rise time T_(r) as shown in equation 16

$\begin{matrix}{T_{r} = {{\left( \frac{{AD}_{{th}\;} - {AD}_{1}}{{AD}_{2} - {AD}_{1}} \right)\left( {t_{2} - t_{1}} \right)} + t_{1}}} & {{Eq}.\mspace{14mu} 16}\end{matrix}$where T_(r) is the rise time, AD_(th) is one of the first A/D valuethreshold and the second A/D value threshold, AD₂ is a first digitalcurrent signal formed when AD₂ exceeds AD_(th), AD₁ is a second digitalcurrent signal immediately preceding AD₁ at time t₁, t₂ is a timecorresponding with AD₂, and t₁ is a time corresponding with AD₁.

In various implementations the controller 60 may generate a single ormultiple threshold current values, including 1, 2, 6, 12, or 24threshold current values. The number of threshold voltages and A/Dthreshold values correspond with the number of threshold current valuesgenerated. Because different voltage vectors applied to the PMSM mayresult in different equivalent inductances, and because differentequivalent inductances affect the rise time as shown in equations 1 and2, the controller 60 may adjust the threshold current to be producedbased upon the particular voltage vector just applied to the PMSM 66.This process of varying the threshold current value allows the risetimes corresponding to all the voltage vectors to be compared on a samebasis. In this specific implementation two threshold currents areproduced by the controller 60 and are related by equation 8. To ensurethe rise times are proportional to the coil inductances of resultingfrom the applied voltage vectors, equations 9 and 10 may be used toconfirm that the correct current threshold value was used and that therise times are in fact proportional to the coil inductances.

Referring back to FIG. 16, a memory 74 is coupled to the rise timemeasurement circuit 72 and stores the plurality of rise times measuredby the rise time measurement circuit 72. The memory may be any disclosedin this document. A rotor-angle estimation circuit 76 is coupled withthe memory 74. The rotor-angle estimation 76 circuit determines therotor position of the PMSM 66 by identifying the voltage vector with theshortest rise time among the plurality of rise time values stored in thememory 74. In other implementations, the rotor-angle estimation circuit76 may determine the rotor position of the PMSM 66 by using averageddata, summed data, or summed data using weighted coefficients asdisclosed in this document. The rotor-angle estimation circuit 76 mayalso be coupled with a controller 60. The rotor-angle estimation circuit76 may communicate the rotor position of the PMSM 66 to the controller60.

In various implementations, the state control section 62, therotor-angle estimation section 76, the memory 74, the rise timemeasurement circuit 72, and the A/D converter 70 may all be included ina microcomputer and their functions carried out on the microcomputerentirely. In other implementations, only portions of their functions maybe carried out using the microcomputer.

A method for sensing a rotor position of a PMSM may be used by variousimplementations of systems for sensing the rotor position of a PMSM. Themethod may include applying a plurality of voltage vectors to stator ofa PMSM. In this implementation, twelve voltage vectors are applied,however, in other implementations 6, 24, or any other number of voltagevectors may be applied to the stator of the PMSM. The method includesgenerating a plurality of sensing current signals from the stator inresponse to the voltage vectors applied to the PMSM. The method alsoincludes converting the sensing current signals into a plurality ofsensing voltage signals using a resistor coupled to the stator, whichmay be a shunt resistor in particular implementations. The methodincludes amplifying the plurality of sensing voltage signals using anamplifier coupled with the resistor and comparing each of the pluralityof sensing voltage signals to a threshold voltage generated by athreshold voltage generator using a comparator coupled with theamplifier. In various method implementations, there may be a singlethreshold voltage or multiple threshold voltages, including 2, 6, 12, or24 threshold voltages. In particular implementations, there is athreshold voltage that corresponds with each sensing voltage signal. Thetwo threshold voltage sensing signals may be related by equations 12 and13, with the first and second threshold currents related by equation 8.The method may include generating the threshold voltage in response toreceiving a command from the controller to the threshold voltagegenerator. In other implementations, the controller itself generates thethreshold voltage.

The method includes calculating a plurality of rise times using theamplified plurality of sensing voltage signals and a signal from thecomparator using a rise-time measurement circuit coupled to thecomparator. The rise time measurement circuit may calculate a pluralityof rise times using the plurality of amplified sensing voltage signalsand a counter. The method may include starting a counter when a voltagevector is applied by the controller, and stopping the counter when thesensing voltage signal is the same as the threshold voltage signal. Themethod includes resetting the counter to measure the rise time of thenext voltage vector applied.

The method includes storing the rise times in a memory which may becoupled with the rise time measurement circuit.

The method of determining a rotor position relative to the stator of aPMSM may be determined using a rotor-angle estimation circuit. Therotor-angle estimation circuit may determine the rotor position byidentifying a voltage vector with the shortest rise time from theplurality of applied voltage vectors. In other implementations, therotor-angle estimation circuit may determine the rotor position by usingaveraged data, summed data, or summed data using weighted coefficientsas previously disclosed in this document.

The method also includes communicating the rotor position to thecontroller by the rotor-angle estimation circuit.

In another implementation of a method for sensing a rotor position of aPMSM, a plurality of voltage vectors is applied to stator of a PMSM. Inthis implementation, twelve voltage vectors are applied, however, inother implementations 6, 24, or any other number of voltage vectors maybe applied to the stator of the PMSM. A plurality of sensing currentsignals from the stator in response to the voltage vectors applied tothe PMSM may be generated.

The method includes amplifying the plurality of sensing current signalsusing an amplifier which may be coupled with the resistor. andconverting each of the amplified sensing current signals to a digitalcurrent signal using an A/D converter coupled to the amplifier.

The method also includes calculating a plurality of rise times using arise-time measurement circuit coupled to the A/D converter and to acontroller, based upon the plurality of digital current signals receivedfrom the A/D converter and at least one A/D threshold value. Inimplementations where two threshold values are used, the A/D thresholdvalue may be calculated using equations 14 or 15. The A/D thresholdvalue is influenced by the voltage threshold values as calculated byequations 12 and 13. The voltage threshold values are influenced by thecurrent threshold values, which relationship is shown in equation 8. Thecontroller may produce 1, 2, 6, 12, 24, or any other number of thresholdcurrents. The number of threshold voltages and A/D threshold valuescorrespond with the number of threshold currents produced. In oneimplementation, the method specifically includes calculating theplurality of rise times by producing a plurality of digital currentsignals from the A/D converter. When the voltage vector is applied, therise-time measurement circuit signals to start the A/D converter. When asensing current signal exceeds the value of the A/D threshold value, thevoltage vector is no longer applied. The rise time measurement sectioncollects the value of the digital current signal that exceeded the A/Dthreshold value, the value of the digital current signal immediatelypreceding the digital current signal that exceeded the A/D thresholdvalue, and the rise times of the two voltage vectors corresponding withthese two digital current sensing signals. The method for calculatingthe rise times includes using these four data to calculate the rise timeas taught in equation 16.

The method may include ensuring the rise times are proportional to thecoil inductances resulting from the applied voltage vectors. Equations 9and 10 may be used to confirm that the correct current threshold valuewas used and that the rise times are in fact proportional to the coilinductances.

The method also includes storing the rise times in a memory which may becoupled with the rise time measurement circuit.

The method determines a rotor position relative to the stator of a PMSMusing a rotor-angle estimation circuit. The rotor-angle estimationcircuit may determine the rotor position by identifying a voltage vectorwith the shortest rise time from the plurality of applied voltagevectors. In other implementations, the rotor-angle estimation circuitmay determine the rotor position by using averaged data, summed data, orsummed data using weighted coefficients as previously disclosed in thisdocument.

The method includes communicating the rotor position to the controllerby the rotor-angle estimation circuit.

In places where the description above refers to particularimplementations of a rotor position sensing system and implementingcomponents, sub-components, methods and sub-methods, it should bereadily apparent that a number of modifications may be made withoutdeparting from the spirit thereof and that these implementations,implementing components, sub-components, methods and sub-methods may beapplied to other rotor position sensing systems.

What is claimed is:
 1. A system for sensing rotor position of apermanent magnet synchronous motor, comprising: a controller configuredto couple with a permanent magnet synchronous motor (PMSM), wherein thecontroller is configured to apply a plurality of voltage vectors to aPMSM to generate a plurality of sensing signals from a stator of thePMSM in response; a rise time measurement circuit configured to coupleto the PMSM, wherein the rise time measurement circuit is configured tocalculate a plurality of rise times using the plurality of sensingsignals; a memory coupled with the rise time measurement circuit,wherein the memory is configured to store the plurality of rise times;and a rotor-angle estimation circuit coupled with the memory, whereinthe rotor-angle estimation circuit is configured to calculate a rotorposition relative to the stator of the PMSM through identifying one of alowest average rise time, a lowest summed rise time, and a lowestweighted summed rise time using the plurality of rise times.
 2. Thesystem of claim 1, further comprising an amplifier coupled to aresistor, wherein the amplifier is configured to receive and to amplifythe plurality of sensing signals to form a plurality of amplifiedsensing signals.
 3. The system of claim 2, further comprising acomparator coupled to the amplifier and to a threshold voltagegenerator, wherein the comparator is configured to receive and tocompare each one of the plurality of amplified sensing signals with athreshold voltage generated by the threshold voltage generator.
 4. Thesystem of claim 3, wherein the threshold voltage generator is coupled tothe controller and is configured to generate the threshold voltage inresponse to a command from the controller, wherein the threshold voltageis one of a first threshold voltage and a second threshold voltage. 5.The system of claim 4, wherein the first threshold voltage and thesecond threshold voltage are calculated using one of a first thresholdvoltage equation and a second threshold voltage equation; wherein thefirst threshold voltage equation isV _(th1)=(G)(R _(sh))(I _(th1))+V _(off) and the second thresholdvoltage equation isV _(th2)=(G)(R _(sh))(I _(th2))+V _(off) where V_(th1) is the firstthreshold voltage, V_(th2) is the second threshold voltage, G is a gainof the amplifier, R_(sh) is a resistance from the resistor, I_(th1) is afirst threshold current, I_(th2) is a second threshold current, andV_(off) is the amplifier's offset voltage.
 6. The system of claim 5,wherein the first threshold current and the second threshold current arerelated by the equation $I_{{th}\; 1} = {\frac{4}{3}{I_{{th}\; 2}.}}$ 7.The system of claim 1, wherein the plurality of voltage vectors is oneof 12 and
 24. 8. The system of claim 1, further comprising an analog todigital (A/D) converter configured to couple to the PMSM, wherein theA/D converter is configured to convert the plurality of sensing signalsinto a plurality of digital current signals.
 9. The system of claim 8,wherein the controller is configured to generate a first A/D thresholdvalue and a second A/D threshold value using one of a first A/Dthreshold value equation and a second A/D threshold value equation;wherein the first A/D threshold value equation is${AD}_{{th}\; 1} = {V_{{th}\; 1}\left( \frac{2^{n}}{{Vref}_{AD}} \right)}$and the second A/D threshold value equation is${AD}_{{th}\; 2} = {V_{{th}\; 2}\left( \frac{2^{n}}{{Vref}_{AD}} \right)}$where AD_(th1) is the first A/D threshold value, AD_(th2) is the secondA/D threshold value, V_(th1) is a first threshold voltage, V_(th2) is asecond threshold voltage, n is the A/D resolution, and Vref_(AD) is afull scale voltage value.
 10. The system of claim 1, wherein the risetime measurement circuit measures each rise time using a rise timemeasurement equation; wherein the rise time measurement equation is$T_{r} = {{\left( \frac{{AD}_{{th}\;} - {AD}_{1}}{{AD}_{2} - {AD}_{1}} \right)\left( {t_{2} - t_{1}} \right)} + t_{1}}$where T_(r) is the rise time, AD_(th) is one of the first A/D valuethreshold and the second A/D value threshold, AD₂ is a first value fromthe A/D converter formed when AD₂ exceeds AD_(th), AD₁ is a second valuefrom the A/D converter formed prior to AD₁ exceeding AD_(th), t₂ is atime corresponding with AD₂, and t₁ is a time corresponding with AD₁.11. The system of claim 1, wherein the controller is configured togenerate a first threshold current and a second threshold current,wherein the first threshold current and the second threshold current arerelated by the equation $I_{{th}\; 1} = {\frac{4}{3}I_{{th}\; 2}}$ whereI_(th1) is the first threshold current and I_(th2) is the secondthreshold current.
 12. A method for sensing a rotor position of apermanent magnet synchronous motor, the method comprising: applying aplurality of voltage vectors to a stator of a permanent magnetsynchronous motor (PMSM); generating a plurality of sensing currentsignals from the stator in response to the plurality of voltage vectorsapplied to the PMSM; converting the plurality of sensing current signalsinto a plurality of sensing voltage signals using a resistor coupled tothe stator; comparing each of the plurality of sensing voltage signalswith a threshold voltage generated by a threshold voltage generatorusing a comparator coupled to the PMSM; calculating a plurality of risetimes using the plurality of sensing voltage signals and a signal fromthe comparator using a rise time measurement circuit coupled to thecomparator; storing the plurality of rise times in a memory coupled withthe rise-time measurement circuit; and determining a rotor positionrelative to the stator of the PMSM using a rotor-angle estimationcircuit by calculating the rotor position relative to the stator bydetermining one of a lowest average rise time, a lowest summed risetime, and a lowest weighted summed rise time using the plurality of risetimes.
 13. The method of claim 12, further comprising generating thethreshold voltage using the threshold voltage generator in response to acommand from the controller coupled with the threshold voltagegenerator, wherein the threshold voltage is one of a first thresholdvoltage and a second threshold voltage.
 14. The method of claim 13,further comprising an amplifier configured to receive and to amplify theplurality of sensing signals to form a plurality of amplified sensingsignals and wherein the first threshold voltage and the second thresholdvoltage are calculated using one of a first threshold voltage equationand a second threshold voltage equation; wherein the first thresholdvoltage equation isV _(th1)=(G)(R _(sh))(I _(th1))+V _(off) and the second thresholdvoltage equation isV _(th2)=(G)(R _(sh))(I _(th2))+V _(off) where V_(th1) is the firstthreshold voltage, V_(th2) is the second threshold voltage, G is a gainof the amplifier, R_(sh) is a resistance from the resistor, I_(th1) is afirst threshold current, I_(th2) is a second threshold current, andV_(off) is the amplifier's offset voltage.
 15. The method of claim 14,wherein the first threshold current and the second threshold current arerelated by the equation $I_{{th}\; 1} = {\frac{4}{3}{I_{{th}\; 2}.}}$16. The method of claim 12, wherein the plurality of voltage vectors isone of 12 and
 24. 17. A method for sensing rotor position of a permanentmagnet synchronous motor, the method comprising: applying a plurality ofvoltage vectors to a stator of a permanent magnet synchronous motor(PMSM); generating a plurality of sensing current signals from thestator in response to the plurality of voltage vectors applied to thePMSM; converting a plurality of sensing current signals into a pluralityof digital current signals using an analog to digital (A/D) convertercoupled to the PMSM; calculating a plurality of rise times, using arise-time measurement circuit coupled to the A/D converter and to acontroller, based upon the plurality of digital current signals receivedfrom the A/D converter and an A/D threshold value from the controller;storing the plurality of rise times in a memory coupled with therise-time measurement circuit; and using a rotor-angle estimationcircuit coupled with the memory to determine a rotor position relativeto a stator by calculating the rotor position relative to the stator bycalculating one of a lowest average rise time, a lowest summed risetime, and a lowest weighted summed rise time using the plurality of risetimes.
 18. The method of claim 17, further comprising generating a firstthreshold current and a second threshold current using the controller,wherein the first threshold current and the second threshold current arerelated by the equation $I_{{th}\; 1} = {\frac{4}{3}I_{{th}\; 2}}$ whereI_(th1) is the first threshold current and I_(th2) is the secondthreshold current.
 19. The method of claim 17, further comprisingmeasuring each rise time with the rise time measurement circuit using arise time measurement equation; wherein the rise time measurementequation is$T_{r} = {{\left( \frac{{AD}_{{th}\;} - {AD}_{1}}{{AD}_{2} - {AD}_{1}} \right)\left( {t_{2} - t_{1}} \right)} + t_{1}}$where T_(r) is the rise time, AD_(th) is one of the first A/D valuethreshold and the second A/D value threshold, AD₂ is a first value fromthe A/D converter formed when AD₂ exceeds AD_(th), AD₁ is a second valuefrom the A/D converter formed prior to AD₁ exceeding AD_(th), t₂ is atime corresponding with AD₂, and t₁ is a time corresponding with AD₁.20. The method of claim 17, wherein the plurality of voltage vectors isone of 12 and 24.